The present invention relates to a zoom lens and particularly to a zoom lens that is used in an interchangeable lens of a single lens reflex camera and the like and has a high variable magnification ratio ranging from a wide angle to a medium telephoto or telephoto range.
Conventionally, as a zoom lens that is used in an interchangeable lens of a single lens reflex camera and the like and has a high variable magnification ratio covering a range of focal lengths from wide-angle to medium telephoto or telephoto, the following zoom lens, including those disclosed in JP-A-8-220439, JP-A-2003-177317, or JP-A-2003-241097, is well known: The zoom lens includes, from an object side in the following order, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power. The reasons why such a configuration is employed include the following: It is easy to increase a variable magnification ratio; and it is possible to downsize the overall length thanks to the configuration in which the positive groups precede.
On the other hand, as the use of digital single lens reflex cameras has become widespread in recent years, what is required is an interchangeable lens optimized for a camera that has an image pickup element with a small image circle for 35-mm silver halide films and the like. As for such a digital-camera interchangeable lens, a higher resolution is required than for a conventional interchangeable lens for 35-mm silver halide films, and the tolerable level of chromatic aberration is also smaller.
Moreover, the ratio of the back focus to the focal length of the entire system has become larger, and, in general, the power arrangement is increasingly necessary to be that of retrofocus.
Moreover, as for a conventional zoom lens having a high variable magnification ratio, resolution is particularly lower at a telephoto end than at a wide angle end due to the effect of chromatic aberration of magnification and the like. Therefore, much higher resolution is required.
Furthermore, in terms of the specifications of the zoom lens, what are required are a much higher variable magnification ratio, a reduction in the shortest shooting distance, and the like, as well as both downsizing and lower costs.